“Green” solvents, such as certain alcohols, acetates, esters, etc. are regarded as such because of their sources of origin (non-petroleum based) and the fact that they biodegrade readily after use without environmental damage. All solvents are classified as Volatile Organic Compounds due to their photo-reactive qualities and Hazardous Air Pollutant (HAPS) status. They are further sub-classified based upon their vapor pressures, boiling points and flash points. The flash point is significant because it is the point at which the liquid becomes a volatile vapor, mixes with oxygen and thereby acquires its most combustible or flammable state. In the United States, the Environmental Protection Agency (EPA) and the Department of Transportation (DOT) have classified such compounds based on their volatilities or “flash points”.
The EPA and DOT Volatile Organic Compound (“VOC”) classifications are as follows:
Class I liquids (flammable)flash point at or below 100° F.Class II liquids (combustible)flash point from 100° F. to below 140° F.Class III liquids (combustible)flash point above 140° F. to below 200° F.
Obviously, the more flammable a solvent, the more restrictions exist on its use. The Federal Government has classified such solvents as Hazardous Materials or “HAZMATS”. Further, manufacturers that utilize solvents must handle the more volatile liquids more carefully and have to address issues involving atmospheric volatility, shelf life and worker health concerns from prolonged exposure to these chemicals. “Green” solvents are usually more costly than petroleum based solvents and may be less effective as solvents than those based on petroleum hydrocarbon stock. However, if these solvents can be modified so that their flash points can be raised, this would result in significantly more uses for these compounds as well as increasing their shelf lives. It is desirable therefore to raise the flash points of a variety of green solvents without substantially increasing the cost of these solvents. This would expand the range of potential uses for and improve the overall solubility of the green solvents.
Some examples of green solvents include, but are not limited to, alcohols such as methanol, ethanol, benzyl alcohol, and turpentine. The problem with these alcohols, however, is that due to their high VOC, they are considered HAPS which violate Federal and State emissions regulations.
Green solvents include, for example, ethyl lactate, with a flash point of 115° F., which although not considered a Class I VOC, still places limitations on their potential uses. Green esters, such as N-butyl propionate, ethyl lactate, methyl soyate, and terpene alcohols, are considered combustible, having flash points ranging from 115° F. up to 250° F. However, they are slow to evaporate and exhibit good solvating characteristics when used in blended compounds. Nonetheless, they are considered environmentally clean and would be utilized more extensively if their volatilities can be reduced.
Many terpene alcohols have the chemical formula: C10H18O. Terpenoid is the name given to the more general class of compounds which are characterized by a repeating carbon skeleton of isoprene. Terpenoids are derived from plants, trees, flowers, and other vegetation which allows their classification as “green compounds”. They come in the form of liquids, solids, waxes, oils, and alcohols. Terpenoids are divided into groups determined by the number of carbon atoms and repeating isoprene units. They may be formed as acyclic, monocyclic, or polycyclic structures.
Terpene alcohols in various forms have been used for centuries in fragrances due to their compatibility with other compounds and their minimal negative environmental impact. The flavor and fragrance industries divide terpineols, which are a type of terpene alcohol, into alpha-, beta- or gamma-terpineols, with Beta-Terpineol being non-naturally occurring. Terpene alcohols have been used for other purposes, such as disinfectants, cleaning compounds, soaps, cosmetics and colognes. They are also known to add, enhance or mask the odor of products which perhaps might be offensive to humans or animals.
U.S. Pat. No. 7,273,839 B2 discloses the use of an alpha terpineol with petroleum based organic solvents and blends of solvents to increase the flash points of these solvents. The patent discloses that the addition of at least 10%, by weight, of an alpha terpineol to a single solvent or combination of solvents increases the flash point of the blended compound. They show examples and claim that at least 5% of one alpha terpineol increases the flash points of specific solvents to useful levels. In one example, they claim that by adding 18 wt % of alpha terpineol to acetone, they increased the solvent's flash point from 0° F. to 143.6° F. However, excessive alpha terpineol loadings (10-18%) cause rapid settling and poor shelf life which substantially adds to the cost of a solvent or combination of solvents. This is therefore a rather costly means to raise flash points.
The excessive loading (i.e., in excess of 10-15% by weight) of a single alpha terpineol results in paint and adhesive formulating problems due to incompatibility with some key resins that shows up during film formation and drying. The formulation often separates, leaving the terpineol behind. The terpineol acts as a diluent, phase separates, perhaps forming under the film, within the film, and upon the surface. The result for fast drying lacquers, vinyls, and similar coatings was complete rejection of the coating by the substrate. After 2-3 days of drying time, the stressed films lifted and floated, exhibiting no ultimate adhesion or bond strength. Vinyls heavily loaded with terpineol perform the worst, because they are in a ketone solvent solution and exhibit a low molecular weight during application. As soon as the ketone based solvents evaporate, the film becomes stressed due to the higher molecular weight of the vinyl resin and the film simply delaminates from the surface. In this instance, a heavy loading of the terpineol acts like a parting agent (or wax) thus preventing permanent adhesion of the vinyl film to the substrate.